The combined powers of three of NASA's Great Observatories -- the Hubble
Space Telescope, the Chandra X-ray Observatory, and the Spitzer Space
Telescope -- have been used to find evidence of a hidden population
of
supermassive black holes in the universe.
All these space telescopes
took a long look at a small region of the sky (called the Great
Observatories Origins Deep Survey field, or the GOODS field for short).
When visible light and X-ray light from this region were compared,
astronomers found numerous X-ray sources that can be identified
as
supermassive black holes in young galaxies billions of light years
from
Earth. But the X-ray glow from other sources had no obvious host
galaxies in optical light. Two of these X-ray sources are identified
by
the central blue spots in the composite Hubble-Chandra images on
the
upper and lower left panels.

The Chandra-Spitzer composite X-ray/infrared images on the upper
and
lower right panels demonstrate that these mysterious sources are
also
detected at infrared wavelengths. This indicates that the galaxies
around these supermassive black holes are heavily obscured by dust.
Visible light is absorbed by the dust, which is heated by the absorption
and glows at infrared wavelengths.

Astronomers have suspected that many supermassive black holes may
have
been missed in optical surveys because they were shrouded in dust.
Combined data from Chandra, Spitzer and Hubble should soon yield
a much
more complete census of the number of black holes in the early universe